1. Field of the Invention
The present invention relates to a driving circuit, and more specifically, to a driving circuit for a plasma display panel (PDP).
2. Description of the Prior Art
In recent years, there has been an increasing demand for planar matrix displays such as plasma display panels (PDP), liquid-crystal displays (LCD) and electroluminescent displays (EL display) in place of cathode ray tube terminals (CRT) due to the advantage of the thin appearance of the planar matrix displays.
In a PDP display, a sustaining discharge pulse activates inert gas to generate ultraviolet so that the ultraviolet further activates fluorescent materials and visible light is emitted to display. As far as the PDP display is concerned, it is required to apply a high voltage to the electrodes. In particular, a pulse-duration of several microseconds is usually adopted. Hence the power consumption of the PDP display is quite considerable. Energy recovering (power saving) is therefore sought for. Many designs and patents have been developed for providing methods and apparatuses of energy recovering for PDPs. One of the examples is U.S. Pat. No. 5,828,353, “Drive Unit for Planar Display” by Kishi, et al., which is included herein by reference.
Please refer to FIG. 1. FIG. 1 is a block diagram of a prior art driving circuit 100. The plasma panel display can be taken as a panel equivalent capacitor Cp. The conventional driving circuit 100 includes four switches S1 to S4 for passing current, an X-side energy recovery circuit 110 and a Y-side energy recovery circuit 120 for charging/discharging the panel equivalent capacitor Cp from the X side of the panel equivalent capacitor Cp and the Y side of the panel equivalent capacitor Cp respectively. S5, S6, S7 and S8 are switches for passing current. D5, D6, D7 and D8 are diodes. V1 and V2 are two voltage sources. C1 and C2 are capacitors adopted for recovering energy, and L1 and L2 are resonant inductors. The X-side energy recovery circuit 110 includes an energy-forward channel comprising the switch S6, the diode D6 and the inductor L1, and an energy-backward channel comprising the inductor L1, the diode D5 and the switch S5. Similarly, the Y-side energy recovery circuit 120 also includes an energy-forward channel comprising the switch S8, the diode D8 and the inductor L2, and an energy-backward channel comprising the inductor L2, the diode D7 and the switch S7.
Please refer to FIG. 2. FIG. 2 is a flowchart of generating the sustaining pulses of the panel equivalent capacitor Cp of the PDP by the conventional driving circuit 100 illustrated in FIG. 1.
Step 200: Start;
Step 210: Keep the voltage potentials at the X side and the Y side of the panel equivalent capacitor Cp at ground by turning on the switches S3 and S4;
Step 220: Charge the X side of the panel equivalent capacitor Cp by the capacitor C1 and keep the voltage potential at the Y side of the panel equivalent capacitor Cp at ground by turning on the switches S6 and S4; wherein the voltage potential at the X side of the panel equivalent capacitor Cp goes up to V1 accordingly;
Step 230: Supply charge to the panel equivalent capacitor Cp of the PDP from the X side by turning on the switches S1 and S4; wherein the voltage potential at the X side of the panel equivalent capacitor Cp keeps at V1 and the voltage potential at the Y side of the panel equivalent capacitor Cp keeps at ground accordingly;
Step 240: Discharge the panel equivalent capacitor Cp from the X side and keep the voltage potential at the Y side of the panel equivalent capacitor Cp at ground by turning on the switches S5 and S4; wherein the voltage potential at the X side of the panel equivalent capacitor Cp goes down to ground accordingly;
Step 250: Keep the voltage potentials at the X side and the Y side of the panel equivalent capacitor Cp at ground by turning on the switches S3 and S4;
Step 260: Charge the Y side of the panel equivalent capacitor Cp by the capacitor C2 and keep the voltage potential at the X side of the panel equivalent capacitor Cp at ground by turning on the switches S8 and S3; wherein the voltage potential at the Y side of the panel equivalent capacitor Cp goes up to V2 accordingly;
Step 270: Supply charge to the panel equivalent capacitor Cp of the PDP from the Y side by turning on the switches S2 and S3; wherein the voltage potential at the Y side of the panel equivalent capacitor Cp keeps at V2 and the voltage potential at the X side of the panel equivalent capacitor Cp keeps at ground accordingly;
Step 280: Discharge the panel equivalent capacitor Cp from the Y side and keep the voltage potential at the X side of the panel equivalent capacitor Cp at ground by turning on the switches S7 and S3; wherein the voltage potential at the Y side of the panel equivalent capacitor Cp goes down to ground accordingly;
Step 290: Keep the voltage potentials at the X side and the Y side of the panel equivalent capacitor Cp at ground by turning on the switches S3 and S4;
Step 295: End.
Please refer to FIG. 3. FIG. 3 shows a diagram illustrating the voltage potentials at the X side and the Y side of the panel equivalent capacitor Cp, and the control signals, M1 to M8, of the switches S1 to S8 in FIG. 1 respectively. In FIG. 3, the horizontal axis represents the time, while the vertical axis represents the voltage potential. Note that the switches S1 to S8 are designed to close (turned on) for passing current when the control signal is high, and to open (turned off) such that no current can pass when the control signal is low.
Conventionally, the energy recovery (power saving) circuit provides two individual channels of charging and discharging the equivalent capacitor respectively (energy-forward channel and energy-backward channel) for each side of the panel equivalent capacitor Cp. Therefore, the amount of required components is quite large. Furthermore, the area of capacitors C1 and C2 is usually considerable. Hence the cost of energy recovery circuit is not easy to reduce.